libxt_tcpmss.c revision 7ac405297ec38449b30e3b05fd6bf2082fd3d803 
1/* Shared library add-on to iptables to add tcp MSS matching support. */
2#include <stdbool.h>
3#include <stdio.h>
4#include <netdb.h>
5#include <string.h>
6#include <stdlib.h>
7#include <getopt.h>
8
9#include <xtables.h>
10#include <linux/netfilter/xt_tcpmss.h>
11
12static void tcpmss_help(void)
13{
14	printf(
15"tcpmss match options:\n"
16"[!] --mss value[:value]	Match TCP MSS range.\n"
17"				(only valid for TCP SYN or SYN/ACK packets)\n");
18}
19
20static const struct option tcpmss_opts[] = {
21	{.name = "mss", .has_arg = true, .val = '1'},
22	XT_GETOPT_TABLEEND,
23};
24
25static uint16_t
26parse_tcp_mssvalue(const char *mssvalue)
27{
28	unsigned int mssvaluenum;
29
30	if (xtables_strtoui(mssvalue, NULL, &mssvaluenum, 0, UINT16_MAX))
31		return mssvaluenum;
32
33	xtables_error(PARAMETER_PROBLEM,
34		   "Invalid mss `%s' specified", mssvalue);
35}
36
37static void
38parse_tcp_mssvalues(const char *mssvaluestring,
39		    uint16_t *mss_min, uint16_t *mss_max)
40{
41	char *buffer;
42	char *cp;
43
44	buffer = strdup(mssvaluestring);
45	if ((cp = strchr(buffer, ':')) == NULL)
46		*mss_min = *mss_max = parse_tcp_mssvalue(buffer);
47	else {
48		*cp = '\0';
49		cp++;
50
51		*mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
52		*mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
53	}
54	free(buffer);
55}
56
57static int
58tcpmss_parse(int c, char **argv, int invert, unsigned int *flags,
59             const void *entry, struct xt_entry_match **match)
60{
61	struct xt_tcpmss_match_info *mssinfo =
62		(struct xt_tcpmss_match_info *)(*match)->data;
63
64	switch (c) {
65	case '1':
66		if (*flags)
67			xtables_error(PARAMETER_PROBLEM,
68				   "Only one `--mss' allowed");
69		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
70		parse_tcp_mssvalues(optarg,
71				    &mssinfo->mss_min, &mssinfo->mss_max);
72		if (invert)
73			mssinfo->invert = 1;
74		*flags = 1;
75		break;
76	default:
77		return 0;
78	}
79	return 1;
80}
81
82static void tcpmss_check(unsigned int flags)
83{
84	if (!flags)
85		xtables_error(PARAMETER_PROBLEM,
86			   "tcpmss match: You must specify `--mss'");
87}
88
89static void
90tcpmss_print(const void *ip, const struct xt_entry_match *match, int numeric)
91{
92	const struct xt_tcpmss_match_info *info = (void *)match->data;
93
94	printf("tcpmss match %s", info->invert ? "!" : "");
95	if (info->mss_min == info->mss_max)
96		printf("%u ", info->mss_min);
97	else
98		printf("%u:%u ", info->mss_min, info->mss_max);
99}
100
101static void tcpmss_save(const void *ip, const struct xt_entry_match *match)
102{
103	const struct xt_tcpmss_match_info *info = (void *)match->data;
104
105	printf("%s--mss ", info->invert ? "! " : "");
106	if (info->mss_min == info->mss_max)
107		printf("%u ", info->mss_min);
108	else
109		printf("%u:%u ", info->mss_min, info->mss_max);
110}
111
112static struct xtables_match tcpmss_match = {
113	.family		= NFPROTO_UNSPEC,
114	.name		= "tcpmss",
115	.version	= XTABLES_VERSION,
116	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
117	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
118	.help		= tcpmss_help,
119	.parse		= tcpmss_parse,
120	.final_check	= tcpmss_check,
121	.print		= tcpmss_print,
122	.save		= tcpmss_save,
123	.extra_opts	= tcpmss_opts,
124};
125
126void _init(void)
127{
128	xtables_register_match(&tcpmss_match);
129}
130